As the trend towards greater reliability of components increases, especially those which may be subject to extremes of either normal operating conditions or accident conditions, so an equivalently greater reliability must be placed on the essential services supplied to these components. Cables supplying electrical power to such components can prove to be unreliable in certain circumstances.
For example when a fire occurs, the cable insulation is frequently burnt or melted allowing the conductors to short-circuit. This short-circuiting could have two adverse effects. Firstly, it could start additional fires. Secondly, it could immobilize essential electrical equipment, e.g. lighting, fire fighting pumps, electrically operated fire or escape doors, and the like.
Another example involves the use of electrical cables inside a nuclear reactor to operate coolant pumps, mensuration equipment, safety devices and the like. Combined gamma and neutron bombardment can cause the occurrence of either cross-linking or scission of the insulating material of the cables, thus changing the properties of the insulating material. Both these factors can lead to embrittlement of the insulating material causing it to crack and hence possibly cause a short circuit when movement occurs due to thermal cycling.
Further, in a water-moderated reactor, the complete loss of coolant could lead to a meltdown, a temperature of 1,000.degree. C. and hydrogen (and other) fires. The electrical cables needed to supply power to mechanisms for the operation of control rods to shut down the reactor and the electrical cables needed to monitor the movement of the control rods would be subjected to such an environment. Also, it is possible that a fault in one of the control motors or mechanisms could lead to a short circuit in a cable which might cause high currents to flow in the cable and the resultant electromagnetic force developed may cause damage to the cable.
There is thus a need for an electrical cable capable of operating in extremely hostile environments on both a permanent and occasional basis.